1. Field of the Invention
The present invention relates to the field of retrofitting parking brakes on high performance sports automobiles.
2. Description of the Prior Art
Sports automobile enthusiasts often seek to modify their vehicles to test the limits of their capacity. In search of drawing the highest performance possible out of their cars, these enthusiasts realize that many of the support components also require modification or outright replacement to withstand the increased rigors of high performance. Knowledgeable sports car enthusiasts often increase the horsepower and acceleration of sports car engines beyond what the original engineering specifications. Consequently components such as the braking system should be upgraded to meet the higher demands for stopping power. Also, many aging models of sports cars incorporate worn components which are out of production and for which no parts are available for replacement.
One particular popular high end automobile that that lends itself to modification is the Porsche Model 914. Enthusiasts of the Porsche 914 often seek to increase the horsepower output of this rear wheel drive platform where rear wheel braking is critical. The original brake system for the Porsche 914 employed a combination main brake incorporating a parking brake function. While these original equipment manufacturer (OEM) brakes were sufficient for the performance of the stock model sold, modified versions of the Porsche 914 require higher braking performance which often leads to greater heat generation thus requiring more efficient heat dissipation.
Age, deterioration, improved braking requirements and unavailability of replacement OEM brakes often force the enthusiast to employ special manufactured disc-braking systems capable of achieving improved braking performance. The better performing disc brake systems for sports cars employ main brakes with hydraulically actuated action calipers and a floating spot-type caliper design for the parking brake. One of the primary advantages of the spot-type floating caliper disc brake is the ability to resist warping that is typically associated with non-spot-type caliper brakes from uneven engagement of the disc. The braking horse power necessary to slow down these modified sports cars on the main brake requires a large braking surface that already covers a large portion of the rotor arc. This is evident where OEM main brakes utilize only two pistons to actuate the calipers compared to the four or six pistons used by upgraded main brakes. Consequently, the main braking system does not have room for an additional parking brake.
A shortcoming of high performance braking systems is that they typically do not incorporate a separate parking brake system. Using a special manufactured main brake leaves the sports car modification enthusiast with three alternatives for a secondary brake. Either a parking brake function can be incorporated into the main brake or an entirely separate parking brake assembly can be mounted or a parking brake can be omitted altogether.
Most replacement main brakes require a hydraulic system and are already too large to incorporate a separate parking brake function. When retrofitting a separate parking brake (often called secondary or emergency brake), typically a drum brake requiring its own bulky mechanical subassembly is used. Most parking brakes use drum systems because there is no room to fit another hydraulic system on the wheel housing for the parking brake so drum brakes use existing mechanical components for actuation. However, using a drum brake as a parking brake requires separate tools for changing the brake shoes, requires a lengthy process for mounting the brake assembly and changing brake linings, and provides inferior braking power than a disc brake system. High performance automobiles require high performance braking. High performance braking usually requires a disk braking system that is not typically available in secondary brake systems. Secondary brakes must achieve two important functions in high end automobiles.
The first function is to assist in keeping the car in place while it is not in gear. This function lessens the strain placed on transmissions when the car is not moving or idling. It is very important to apply the secondary brake when a car with standard transmission is parked on an incline. Without it, the car is free to roll down the hill. Oftentimes one can recognize an automobile in which the OEM brake has been replaced since the consequent lack of a brake dictates the placement of a brick or other obstruction on the down hill side of a hill.
The second function of a parking brake is to serve as a secondary brake or emergency back up brake should the main brake fail. Without a secondary brake, failure of the main brake usually spells disaster since the motorist must then downshift to decelerate placing him or her at risk of failing to stop before disaster. As most sports car enthusiasts know, employing an OEM secondary brake to decelerate from high speeds runs the risk of the parking brake exceeding the capacity of the mount to withstand stress. While drum brakes are typically sufficient for use in non-sports cars, their weaker braking power and bulkiness detracts from the braking required in high end sports cars. I have discovered that by employing a spot-type disc brake for an emergency brake, braking power is improved and reliability of the brake mount is improved.
As one skilled in the art of modifying sports autos knows, seldom is the framework of an automobile conducive to non-OEM parts since the automobiles were designed as complete systems with many hours of design and engineering exerted in the elaborate interconnection of components to achieve ease of assembly and performance efficiency. Consequently, non-OEM parts often do not lend themselves to ready and convenient mounting from a wheel or wheel hub thus requiring the framework itself to be modified for receipt of the new part. Modification of the framework typically involves mutilating the components by welding and cutting metal. Disc brake systems are typically subject to these constraints and sports car enthusiasts wishing to employ high performance disc brakes on, for example, the Porsche 914 are forced to modify the components surrounding the suspension near the wheels requiring undesirable expenditures of time, money, and risk in the damage of the suspension components.
In recognition of the need for auxiliary brakes, it has been proposed to attach non-OEM disc brakes to automobile wheels. One proposed mount is observed in the U.S. Pat. No. 6,478,120 to Runkel et al. The patent to Runkel discloses an actuating apparatus with automatic clearance adjustment for vehicles using a disc brake system. The actuating apparatus uses a spot-type brake having a floating caliper. A lever is fastened to the outer end of the shaft and connected to a parking brake lever or pedal for switching the operation of the brake from main brake to parking brake mode. For attachment to the suspension, the caliper is guided onto the brake carrier so as to be in a conventional manner displaceable parallel to the axis of a brake disc. Brakes of such design suffer from a lack of secured and convenient mounting means to the suspension. While they can be guided into place, their attachment requires the modification of OEM suspension components or an OEM design that incorporates the brake in its current form. Additionally, combination brakes such a Runkel's are bulky and do not fit onto the suspension and rotor of a high end sports car wheel where two separate brakes are necessary.
U.S. Pat. No. 5,038,895 to Evans discloses a disc brake assembly that can function as both a hydraulically operated main brake and a mechanically actuated parking brake. Like Runkel's brake, the brake to Evans suffers from bulkiness and even more importantly, should the main brake pad fail, the secondary brake system is likely to also fail since they operate using the same brake pads. To the further detriment of one using Evans' brake, the system lacks a convenient and simple retrofit mounting structure that can be mounted onto an existing automobile wheel housing.
These proposed solutions in the prior art require modifying or mutilating the wheel assembly or are designed as their own OEM brake systems uncooperative for retrofitting. These solutions lack ease of installment and readiness to a preexisting wheel housing. Other related art may suggest means for mounting to a wheel housing but does not take advantage of preexisting bores outside of the wheel hub where it is less complex to mount on. Also, while the prior art references teach combining a parking brake to a main brake, many fail to suggest using separate brake pads for the main and secondary braking functions in the event the main brake should fail.
Therefore, it can be seen that a need exists in the art for a brake kit that is readily mountable to existing automotive wheel structure to provide high performance secondary braking.